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Custom Mechanical System Measures

Mechanical system energy efficiency measures include customized upgrades to HVAC systems, hood controls, energy management systems (EMS), and others. Green star central Air Conditioning Contracting has an in-house staff of engineers and technical experts who have over 30 years’ experience performing large, complex, and comprehensive projects for commercial, industrial, and municipal customers.

  • HVAC controls
  • Exhaust Hood controls


HVAC controls

Heating, ventilating, and air conditioning (HVAC) systems use 50-60% of the total energy consumed in buildings. HVAC systems heat, cool, and ventilate a building to maintain proper airflow, air quality, and overall comfort conditions for its occupants. Green star central Air Conditioning Contracting installs cost-saving HVAC controls, including variable frequency drives, demand controlled ventilation, EC motors and controls, and economizers.

Variable frequency drives

Variable frequency drives (VFDs) are designed primarily to optimize the speed of a motor. Motors that power pumps and fans will run at full speed regardless of whether or not the mechanical system component requires full power to operate. VFDs vary the motor speed based on system feedback, so only the actual power needed is consumed. Varying the speed optimizes the energy consumed to eliminate wasted energy and costs.

A cubic relationship exists between the reduction in motor speed and the energy the motor consumes, according to affinity laws. For example, if the speed of a motor is reduced by 15 percent, the motor horsepower is reduced by 45 to 50 percent. In some instances, a VFD can save 50% of the energy required to perform an operation. Other benefits of a VFD include:

  • Reduced fan noise
  • Reduced electric demand (kW)
  • Reduced wear and tear
  • Reduced maintenance
  • Power factor correction
  • Soft start

Demand controlled ventilation

A demand controlled ventilation (DCV) system adjusts the amount of fresh air that is brought indoors based mainly on the number of occupants within a room or space. Ventilation is important for buildings to prevent air quality issues from excessive carbon dioxide (CO2), odors, and off-gassing (trapped gas in materials and furniture). DCV deploys CO2 sensors in return air ducts to measure CO2 levels against predetermined set points. When CO2 levels rise above the prescribed setpoint, controls are triggered, opening air dampers or commanding fans to bring in and circulate additional fresh air until CO2 levels are reduced sufficiently. Without DCV, most buildings need to be ventilated with constant airflow, regardless of the building’s occupancy level.

Fresh air introduced into building needs to be heated or cooled, depending on the season, to maintain comfort conditions for occupants. Conditioning more air than necessary results in a great deal of wasted energy. Conversely, monitoring CO2 also ensures that ventilation occurs as necessary to satisfy building code requirements and to maintain comfort conditions. A DCV system can reduce energy use for this specific measure between 30-50% with typical paybacks of less than 2 years.

Commercial and industrial sectors that benefit the most from a DCV system include:

  • Office Buildings
  • Schools & hospital
  • Hospitals
  • Hotels
  • Food services
  • Shopping malls

HVAC economizers

An HVAC economizer system will sense the inside and outside air temperatures. If the temperature of the air outside the building is cool and dry enough to utilize for air conditioning, the economizer will turn off the compressor and utilize the outside air. This process can reduce energy use for this specific measure by up to 30% annually with a typical payback of 1-2 years.

Exhaust Hood Controls

Ventilation can account for up to 29% of a kitchen’s energy bill. Per square foot, restaurants use about 2.5 times more energy than other commercial buildings. Kitchen exhaust hoods are important for removing heat, smoke, odors, and particulates from the cooking area to prevent them from exiting the kitchen and infiltrating other areas of the building, such as the dining room. It is critical to have a well-ventilated kitchen, combined with an efficient HVAC system, for employee and patron safety and comfort.

Exhaust hood fan motors without controls usually run at full speed, even during times when little to no cooking occurs. When kitchens are less busy, exhaust hood motors need not run at full speed. Specialized exhaust hood variable-speed drives (VSDs) can be installed on exhaust fan motors, as well as the makeup air unit, to regulate the speed of the fans based on the temperature, smoke, and/or air quality in the exhaust hood. Using sensors, VSDs adjust the speed of the exhaust fan motor. This simple upgrade can reduce energy use between 20-50% for this specific measure, while quieting operations during slower periods.

Exhaust hood controls also reduce maintenance costs in a few different ways:

  • Slows down the motors to reduce wear and tear
  • Reduces the amount of makeup air required to be brought into the space and conditioned
  • Lessens the strain on the heating and cooling system
  • Slows down the motors, allowing the grease to flow back to the hood to collect in the grease cups, rather than it remaining in the ducts and exhaust
  • Reduces the frequency with which the system must be cleaned

Customers who make upgrades with energy efficient exhaust hood controls typically see a return on investment in less than two years. Types of businesses that benefit from exhaust hood controls include:

  • Office Buildings
  • Schools & hospital
  • Hospitals
  • Hotels
  • Food services
  • Shopping malls

To send us your enquiry, please contact us.